FIG. 1 and FIG. 2 are respectively perspective views indicating magnetic head units of the prior art. FIG. 3 shows the bottom view of the magnetic head unit shown in FIG. 1 and FIG. 2.
In FIG. 1 and FIG. 3, A indicates a R/W head; 1 is one core of the R/W head A; 2 is the other core thereof, M is gap formed between both cores 1 and 2; 8 is R/W coil of R/W head A wound on said core 1. B is a first Er head provided at one side of said R/W head A. 3 and 4 are a pair of cores forming said head B; N.sub.1 is gap between both cores 3 and 4; C is the second Er head provided at the other side of R/W head A; 5, 6 are a pair of cores forming said second Er head; N.sub.2 is gap between both cores 5 and 6; 9 is a common Er head for Er heads B, C wound on said cores 3 and 5; 10 is a R/W back core bridging the upper ends of cores 1, 2 of R/W head A; 11 is an L-shaped Er back core capped on the Er coil 9 which has the structure, for equalizing the intensity of field of the two Er heads B and C, that a constant space is kept through the Er coil 9 between the upper end surface of the cores 3, 5 of both Er heads B and C and the Er back core 11. 7 is a slider which is composed of barium titanate ceramic and is slidingly in contact with a disc D. At the sliding surface with said disc D, the gap M of R/W head A and gaps N.sub.1, N.sub.2 of Er heads B, C are formed as shown in FIG. 3. Here, 23, 24 and 25 are spacers consisting of ceramic etc. formed on the same plane as said gaps N.sub.1, M, N.sub.2.
However, since the magnetic head unit of the prior art has a structure that a constant space is kept between the cores 3, 5 of Er heads B, C and the Er back core 11, it has the disadvantage that it is difficult for assembling to obtain such constant space. This difficulty has an adverse effect on magnetic efficiency and leak of magnetic flux easily generates distortion of waveform.
Moreover, as shown in FIG. 2, it is also known to employ the structure that one Er back core 21 is bridged to the side surface of a pair of cores 3, 4 forming one Er head B, while the other Er back core 22 is bridged to the side surface of a pair of cores 5, 6 forming the other Er head C. However, this structure results in such disadvantage that a pair of Er back cores 21, 22 are required, namely the number of parts increases and simultaneously the number of assembling steps also increases. The Er back cores 21, 22 are easily displaced vertically and horizontally from the specified position at the time of assembling; such displacement causes fluctuation of head characteristics and moreover magnetic flux leaks from the upper end of Er cores 3, 5.